Direct current air curtain

ABSTRACT

Direct current air curtains are provided, which may be used to help reduce or prevent the exchange of heat between different areas. The direct current air curtain may be used in a variety of applications, including trailers, rail cars, vehicles and containers.

This application claims the benefit of U.S. Provisional Application No.61/252,925, filed Oct. 19, 2009.

FIELD

The present embodiments relate to direct current air curtains for use intransportation devices, including trailers, rail cars and containers.

BACKGROUND

In many commercial applications, it is desirable to maintain multipleareas at different temperatures. Maintaining this difference intemperature between two areas is complicated when it is necessary tomove items between the areas. This is particularly true with thetransportation of refrigerated or frozen goods.

Various methods and devices have been developed to address thischallenge. In some cases, strips of plastic sheeting may be hung in anopening dividing two areas of various temperatures to reducedifferential air flow between the areas while still permitting themovement of goods. While these strips help reduce heat exchange, theyinterfere with easy movement between the areas. Other designs involvetwo sets of doors between the colder and warmer areas, the doors beingoffset from one another and designed so that only one set of doors maybe open at any given time. These offset doors require an intermediatespace between the doors, and thus may not be suitable when space islimited.

Another method of limiting the exchange of heat between areas has beento employ air curtains. Some exemplary air curtains include thosedescribed in U.S. Pat. Nos. 6,112,546 and 6,874,331, which areincorporated herein by reference. Typically, air curtains slow theexchange of heat by using fans to blow air across an opening between twoareas. The air flow is directed more or less parallel to a plane definedby the opening thereby creating a vertical wall of fast moving air thatseparates the two different temperature areas. The air curtain preventsor reduces the flow of air between the two areas. Most air curtains aredesigned for fixed applications (such as walk-in coolers) and they aredesigned to run on alternating current power sources. In addition, thesize of the air curtain and the noise generated by the motor are lessimportant in fixed applications than in mobile applications (such as arefrigerated trailer).

In the fields of transportation of refrigerated and frozen goods,efforts to prevent heat exchange at openings and doors have typicallybeen limited by restrictions on the space available. For instance, somevehicles have employed the plastic strips described above; however,double doors are generally not practical. Also, because vehicles are notconnected to a power grid, alternating current power sources aregenerally not available and the relatively low voltage direct currentgenerated by a tractor trailer presents unique design challenges.

BRIEF SUMMARY

Direct current powered air curtains suitable for use in trailers, andother vehicles or containers, are presented. The direct current aircurtains may include any of the following aspects in variouscombinations and may also include any other aspect described below inthe written description or shown in the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a perspective view of an embodiment of a direct currentair curtain;

FIG. 2 depicts a bottom view of an embodiment of the direct current aircurtain;

FIG. 3 depicts a cross-sectional view of an embodiment of the directcurrent air curtain along line A-A as indicated in FIG. 2;

FIG. 4 depicts an exploded view of an embodiment of the direct currentair curtain showing a direct current motor, a connection and atangential fan;

FIG. 5 depicts an exemplary refrigerated trailer having one embodimentof the direct current air curtain placed above a side door to thetrailer;

FIG. 6 depicts a closer view of an embodiment of the direct current aircurtain and trailer door of FIG. 5; and

FIG. 7 depicts a side view of an embodiment of the direct current aircurtain within a trailer.

DETAILED DESCRIPTION OF THE DRAWINGS

A direct current air curtain (“DC air curtain”) will be described withreference to FIGS. 1-7. While the DC air curtain is generally depictedand described in association with a trailer, it is contemplated that theDC air curtain may have other applications, including, but not limitedto, walk-in coolers, rail cars, vehicles and portable containers.

FIG. 1 shows a perspective view of a DC air curtain 10. As will beexplained in association with the figures, the DC air curtain 10 pullsair into the housing 16 through air intakes 14 (e.g., air inlets 14) andthen expels the air through the air outlet 12 to generate a wall of air.

FIGS. 2-4 present various views of the DC air curtain 10 and itsinternal parts. These figures are discussed together in explaining theoperation of an embodiment of the DC air curtain 10. The DC air curtain10 is driven by a DC motor 18, which is shown in FIG. 4. The DC motor 18connects to one or more tangential fans 20, so that when in operation,the fans 20 may generate the air flow required of the air curtain 10.The DC motor 18 may be a brushless DC motor, or any other type of DCmotor known to persons of ordinary skill. In some embodiments, the DCmotor may also be a moisture tight motor. Further, it should beunderstood that the DC motor 18 may have a drive shaft 22 that emergeson one end of the motor 18 or both ends of the motor 18, as shown inFIG. 4.

The tangential fan 20 may connect to the drive shaft in any of a numberof different ways. As illustrated, the tangential fan 20 connects withthe DC motor 18 using a connecting plate 24 with a collar that fits overa first end of the drive shaft 22. The connecting plate 24 may attach tothe tangential fan 20 and the drive shaft 22 in any known method,including mechanical fasteners, adhesives, and threaded connections.While not shown in FIG. 4, it is contemplated that a second tangentialfan 20 may attach to a second end of the drive shaft 22. That is, asingle DC motor 18 may be used to drive two tangential fans 20simultaneously through the use of a drive shaft 22 that extends fromeach end of the motor 18.

The DC motor 18 and tangential fans 20 of FIG. 4 are contained withinthe housing 16 shown in FIGS. 1-3. When multiple tangential fans 20 areused, one on each end of the DC motor 18, it may be desirable for thefans 20 to be equally sized such that the DC motor 18 is disposed in thecenter of the housing 16. Although not illustrated, it should beunderstood that the ends of the tangential fans 20, away from the motor,may be supported within the housing 16 on rotatable bearings.

As illustrated by the arrows in FIG. 3, when the DC motor 18 isactivated, the tangential fan 20 rotates, and the blades 24 of thetangential fan 20 pull air through the air intakes 14 into the housing16. As the tangential fans 20 continue rotating, the blades 24 drive theair through the tangential fan 20 to the inside of the housing 16 andout the air outlet 12 as shown by the arrows in FIG. 3. Some of the airintakes 14 may be rotationally positioned 90 degrees from the airoutlets, as shown in FIG. 1. Therefore, some air is generally pulledinto the housing 16, rotated roughly 270 degrees, and then expelledthrough the air outlet 12.

Some embodiments of the DC air curtain 10 may include a baffle 26 tohelp to divide the air intakes 14 from the air outlet 12 and therebyimprove air flow within the housing 16. Further, an internal wall 30 maybe included within the housing 16 to help direct the flow of air aroundthe tangential fan 20 and towards the air outlet 12. Some embodiments ofthe DC air curtain 10 may include a fin 28 within the air outlet 12 tohelp direct the air flow that generates the wall of air. Alternatively,some embodiments of the DC air curtain 10 may include a nozzle thatdefines the air outlet 12. This nozzle may be reoriented (e.g.,positionable) to direct the air flow.

In operation, the DC motor 18 may use an electronic controller 32. Theelectronic controller 32 regulates the rotational speed of the motor 18,which in turn regulates the rotation of the tangential fan 20 and theflow rate of air being emitted from the DC air curtain 10. As explainedherein, the electronic controller 32 may be in communication with aswitch or sensor to determine when the DC motor 18 should be activatedand also how fast the motor should operate.

FIG. 5 illustrates an embodiment of a DC air curtain 10 mounted within arefrigerated trailer 34. In this figure, the DC air curtain 10 ispositioned above a side door 36 of the refrigerated trailer 34. The DCair curtain 10 may be mounted to the refrigerated trailer 34 using amounting plate 38 on the housing 16 (shown in FIG. 3), which is in turnmounted to the wall 40 of the trailer 34 using devices well known in theart, including mechanical fasteners such as nuts and bolts. In FIG. 5,the DC air curtain 10 is mounted adjacent to (e.g., above) the side door36 in order to create a wall of air that flows from top to bottom.Alternatively, the DC air curtain 10 may be located on a side of thedoor 36 in order to create a wall of air that flows from left to rightor right to left.

The refrigerated trailer 34 includes a refrigeration unit 42, whichcools and circulates air within the trailer 34, thereby preserving andallowing shipment of goods that require refrigeration and/or freezing.Refrigeration units, such as the one shown in FIG. 5, may includealternators and batteries for producing and storing electricity. Thepower generated by the alternator and stored by the batteries may powernot only the refrigeration unit itself, but also other trailer systems,such as lighting within the trailer. The alternator produces, and thebatteries store, direct current electrical power. The alternator mayproduce roughly 65-120 Amps of current at around 11-13 volts potential.In other embodiments, the alternator and batteries may produce roughly23-25 volts potential. In some embodiments, the electrical power used topower the trailer lighting system may also be used to power the DC aircurtain 10.

FIG. 6 shows a close-up view of an embodiment of the air curtain 10within a refrigerated trailer 34. As shown, the DC air curtain 10 ispositioned on the wall 40 of the trailer 34 above an opening 44 for theside door 36. Trailers may range in height from about 95 to 110 inches(2.4 m to 2.8 m). The side doors in such trailers may be around 84inches (2.1 m) tall. Therefore, the housing 16 of the DC air curtain 10may be sized to fit within a space ranging from around 11 to 26 inches(28 to 66 cm) in height. However, other door sizes may be used, and thehousing 16 may be sized accordingly. In one embodiment, the housing 16is 10 inches in height. Furthermore, because the trailer 34 is generallyfilled with goods, it is desirable that the housing 16 maintain a lowprofile. Therefore, the housing 16 may be designed to have a depth of7-12 inches (17.8 to 30.5 cm). The width of the DC air curtain 10 may besized in accordance with the width of the side door 36. In someembodiments, it may be desirable for the DC air curtain 10 to beslightly wider than the door to create a sufficiently large wall of airto prevent heat exchange. In other embodiments, the width of the DC aircurtain 10 may be less than the door width because the wall of air willtend to spread as the air travels away from the DC air curtain 10.Alternatively, the DC air curtain 10 and door 36 may have similarwidths.

In practice, and as noted previously, it is desirable for the DC aircurtain to run when the door 36 is open. Therefore, a sensor 46 may beincluded. The sensor 46 may be of any type known to those of skill inthe art, including, but not limited to, a pressure sensor, light sensor,or electromagnetic sensor. Alternatively, a switch may be placed in thetrailer or truck cab so that the operator may manually turn the DC aircurtain 10 on and off. As shown in FIG. 6, the sensor 46 is a pressuresensor. When the door 36 is closed, a portion of the door 36 or a flangeattached to the door 36 contacts the sensor 46, causing the sensor 46 tosignal the DC air curtain 10 to turn off. In contrast, when the door 36is ajar, the sensor 46 will signal the DC air curtain 10 to turn on,thereby preventing or slowing the exchange of heat with the outsideenvironment. The sensor 46 may be located on a side of, above, or belowthe door 36.

As shown in FIG. 6, when the DC air curtain 10 is in operation, ambientair 48 from within the trailer is pulled into the housing 16 through theair intakes 14. As explained above, the air 48 is then expelled from thehousing 16 through the air outlet 12 in a direction 50 that is generallytowards the floor of the trailer. FIG. 7 depicts a side view of the aircurtain 10 and the door 36. As illustrated, the air 48 is pulled throughthe air curtain 10 and then expelled through the air outlet 12 (visiblein FIG. 2). The air 48 may be expelled from the air outlets 12 at avariety of angles relative to the plane of the door opening 44 (visiblein FIG. 6), although the air 48 is still generally directed towards thefloor of the trailer. In practice, the wall of air generated by the DCair curtain 10 may be directed roughly parallel to the plane of the dooropening or at an angle 52 of as much as around 20 degrees to the planeof the door opening. In one embodiment, the angle 52 is oriented so thatthe direction 50 of air flow is towards the center of the trailer. Otherorientations may also be used.

The wall of air generated by the DC air curtain 10 inhibits the flow ofair between the spaces on either side of the air curtain. While thishelps retain the desired temperature within the refrigerated trailer, itis important that the air curtain not generate so much noise as to makecommunications difficult or create an occupational hazard. Someembodiments of the DC air curtain generate around 85 decibels or lessnoise. Other embodiments produce around 80 decibels or less noise.

To generate the air wall described above, some embodiments of the DC aircurtain 10 generate air flow of roughly between 1000 and 1500 cubic feetper minute (28.3 to 42.5 cubic meters per minute). Other embodimentsgenerate air flow rates of roughly 1100 to 1300 cubic feet per minute(31.1 to 36.8 cubic meters per minute). However, other flow rates may begenerated. Further, the required flow rate will depend upon a number offactors, which may include the size of the opening adjacent the aircurtain and the angle of air flow.

Refrigeration units, such as the ones described above and shown in FIG.5, are commercially available from a variety of manufacturers includingthe SPECTRUM and SB series of products from THERMO KING of Minneapolis,Minn., and the X2 series from CARRIER TRANSICOLD of Farmington, Conn.Those skilled in the art understand that refrigeration units produced byother manufacturers may also be used. Further, a variety of batteriesand power packs may be used in conjunction with the refrigeration units.For example, batteries and power packs are commercially available fromTHERMO KING under the trade name EON and EON POWER PACK.

In some embodiments, the DC motor 18 for the DC air curtain 10 may drawbetween 15 and 40 amps current. In other embodiments, the DC motor 18may draw between 22-35 amps. In still other embodiments, the DC motor 18may be rated at 25 amps. In some embodiments, the DC motor 18 maygenerally require between 200 and 350 watts power. In other embodiments,the DC motor 18 may require roughly 250-300 watts power. The DC motor 18should generate sufficient torque to rotate the tangential fansufficiently fast to generate the required air flow. In someembodiments, the DC motor 18 may generate between approximately 1.5 and2 N·m torque, and in other embodiments, the DC motor 18 may generatebetween 1.6 and 1.7 N·m torque. In some embodiments, the DC motor 18 mayhave rotational speeds of between 1300 and 1700 RPM, and in yet otherembodiments, the DC motor 18 may rotate between 1400 and 1650 RPM. Inanother embodiment, the DC motor may rotate at 1400 RPM. The DC motor 18may have class F insulation; however, as understood in the art, otherclasses of insulation may also be used. In some embodiments, the DCmotor 18 has eight poles, three phases, and four windings per phase.However, those skilled in the art understand that these values may bevaried. Additionally, some embodiments of the DC motor 18 may use Halleffect sensors to communicate rotor position with the electroniccontroller 32.

The electronic controller 32 may use any control method known to thoseof skill in the art, including open loop speed control. The electroniccontroller 32 may receive feedback from the DC motor 18 in any knownmethod. In one embodiment, the electronic controller 32 receives motorfeedback through three Hall sensors at 120 electrical degree spacing.The electronic controller 32 may be rated for a continuous current of 25amps with a peak current of 40 amps. However, controllers rated forother current values may also be used, depending on the current draw ofthe associated DC motor 18. Additionally, the electronic controller 32may include any of the transistor types known to those skilled in theart. In one embodiment, six metal-oxide-semiconductor field-effecttransistors (MOSFET) are used that have a switching frequency of 33 kHz.The electronic controller 32 may be a digital signal controller. Digitalsignal controllers are commercially available, including from MICROCHIPTECHNOLOGY INC. of Chandler, Ariz. (e.g., P/N dsPIC33FJ12MC202-I/SO)

To prevent the electronic controller 32 from short circuiting and toprevent the windings of the DC motor 18 from overheating and burningwhen an obstruction prevents the tangential fan 20 from rotating (e.g.,the tangential fan 20 is frozen), the electronic controller 32 mayinclude a programmable current sense high side switch. The current sensehigh side switch senses current and temperature in the windings of theDC motor 18. Alternatively, a current sense switch senses current andtemperature within the electronic controller 32. When the current sensehigh side switch detects a current or a temperature higher than apredetermined level, the switch shuts off the DC air curtain 10; whenthe obstruction is removed, and the current or the temperature fallsbelow the predetermined level, the switch turns the DC air curtain 10back on. Programmable current sense high side switches are commerciallyavailable, including from INTERNATIONAL RECTIFIER of El Segundo, Calif.(e.g., P/N IR3313PbF).

In one embodiment, the electronic controller 32 is electricallyconnected to a fast acting circuit breaker to further protect the DCmotor 18 and the controller 32 from overload. In one embodiment, thecircuit breaker is a 30 Amp circuit breaker. The circuit breaker mayalso provide reverse battery protection, such that the circuit breakermay be triggered when the batteries are installed backwards (e.g., withreversed polarity). Fast acting circuit breakers are commerciallyavailable, including from CARLING TECHNOLOGIES, INC. of Plainville,Conn. (e.g., P/N AC1-B0-32-630-1G1-C).

The electronic controller 32 may also be programmed for a motor softstart, such that the current through the DC motor 18 is temporarilyreduced at start-up. The current is ramped-up slowly to prevent in-rushcurrent and temporary overloads.

As noted above, the DC air curtain 10 may include a tangential fan.Tangential fans are also commercially available, including from EUCANIAINTERNATIONAL INC. of Dorval, Canada. In one embodiment, the DC aircurtain 10 uses two 5.5 inch diameter (14 cm) and 17.5 inches long (44.5cm) tangential fans that each have 36 blades. However, the size of thefan and the number of blades is dictated by several factors includingthe size of the housing, the volume of air required for a given door,and whether the DC motor 18 has fans on one or both ends. Therefore,other fans may also be used.

While the description generally discuses DC air curtains in conjunctionwith refrigerated trailers, it is contemplated that the DC air curtainsdisclosed herein may be used with other vehicles and containers,including heated vehicles.

It is intended that the foregoing detailed description be regarded asillustrative rather than limiting, and that it be understood that it isthe following claims, including all equivalents, that are intended todefine the spirit and scope of the invention.

1. A system comprising: a refrigerated trailer comprising: a door, thedoor having open and closed positions; and a refrigeration unit attachedto the refrigerated trailer, the refrigeration unit comprising a powersource; and an air curtain comprising: a housing comprising an air inletand an air outlet, the housing being sized to fit within the traileradjacent to the door, the air inlet being offset from the air outlet; adirect current motor attached to the housing; an electronic controllerelectrically coupled to the direct current motor and the power source ofthe refrigeration unit; a fan operatively coupled to the direct currentmotor; and a sensor positioned in the door and in communication with theelectronic controller, wherein the sensor signals the electroniccontroller when the door is in the open position, the electroniccontroller activating the direct current motor to rotate the fan afterreceiving the sensor signal, wherein the fan pulls air from within thetrailer into the housing unit through the air inlet and redirects theair so that the air is expelled through the air outlet.
 2. The system ofclaim 1, wherein the air curtain requires around 12 volts electricpotential and between 20 and 40 amps current.
 3. The system of claim 1,wherein the direct current motor is a brushless direct current motor. 4.The system of claim 1, wherein the air curtain is operable to generatean air flow of between 1000 and 1500 cubic feet per minute.
 5. Thesystem of claim 1, wherein the air curtain is operable within anenvironment having a temperature of between −29 degrees C. and 43degrees C.
 6. The system of claim 1, wherein the air curtain generatesan air flow that is oriented within 0 to 20 degrees of a plane of a dooropening.
 7. The system of claim 1, wherein the air curtain generatesaround 85 decibels or less noise when activated.
 8. The system of claim7, wherein the air curtain generates approximately 80 decibels or lessof noise when activated.
 9. The system of claim 4, wherein the aircurtain generates an air flow of between 1100 and 1300 cubic feet perminute.
 10. The system of claim 1, wherein the power source of therefrigeration unit comprises an alternator and a battery, and whereinthe direct current motor and the electronic controller are powered by anelectrical output of the alternator, the battery, or the alternator andthe battery of the refrigeration unit.
 11. The system of claim 1,wherein the air inlet is offset from the air outlet by roughly 90degrees.
 12. The system of claim 1, wherein the fan is a tangential fan.13. An air curtain comprising: a housing comprising an air inlet and anair outlet; a direct current motor attached to the housing, the directcurrent motor comprising an output shaft; an electronic controllerelectrically coupled to the direct current motor; a sensor incommunication with the electronic controller and configured to signalthe electronic controller to activate and deactivate the direct currentmotor; and a fan positioned within the housing and mechanically coupledto the output shaft of the direct current motor, wherein the air curtaingenerates air flow between 1000 and 1500 cubic feet per minute when inoperation.
 14. The air curtain of claim 13, wherein the air curtaingenerates less than 85 decibels of noise
 15. The air curtain of claim14, wherein the air curtain generates less than 80 decibels of noisewhen in operation.
 16. The air curtain of claim 13, wherein the aircurtain generates air flow between 1100 and 1300 cubic feet per minutewhen in operation.
 17. The air curtain of claim 13, wherein the aircurtain uses approximately 12 volts of electric potential and between 20and 40 amps current.
 18. The air curtain of claim 13, wherein the directcurrent motor is moisture tight.
 19. The air curtain of claim 13,wherein the housing has outside dimensions of approximately 1 m inlength, 25 cm in height and 22 cm or less in depth.
 20. The air curtainof claim 13, wherein the air outlet further comprises a positionablenozzle.
 21. The air curtain of claim 13, further comprising another fan,wherein the output shaft of the direct current motor extends away fromthe direct current motor on each end of the motor, and wherein one ofthe fan and the other fan is mechanically coupled to the output shaftadjacent to each end of the direct current motor.
 22. The air curtain ofclaim 13, wherein the air curtain is operable within an environmenthaving a temperature range of −29 degrees C. to 43 degrees C.
 23. Theair curtain of claim 13, wherein the fan is a tangential fan.